In an automated machining operation it is standard practice to bring the workpiece-gripping chuck to a full stop only rarely. Instead between machining operations the rotating chuck is loosened, the workpiece is moved axially in it, and the chuck is tightened on it so that machining can recommence. In such an arrangement it is therefore necessary to provide a drive which can effect the necessary adjustment movements in the chuck regardless of whether it is rotating or not, and without respect to the rotation speed or direction.
This is typically done by providing a drive motor which is stationary and whose rotary output is connected to a rotation-canceling transmission having a pair of oppositely rotating outputs that are connected to respective inputs on the chuck. These inputs in turn are part of a movement-converting unit in the chuck that transforms the opposite rotations of the inputs into the desired type of movement for the chuck.
In German patent document 3,737,190 filed Mar. 11, 1978 by Karl Hiestand the chuck in question has a jaw-actuating member which is rotated in the chuck body in one direction to tighten the chuck and oppositely to loosen it. Accordingly this chuck is provided with two input gears or sprockets constituting the movement-converting inputs connected to the outputs of the rotation-canceling transmission. One of these sprockets is fixed on the chuck body and the other on the rotary jaw-actuating unit. Such an arrangement does not work with a chuck or the like having an axially displaced jaw-adjusting element. The solid connection of the one input sprocket with the chuck body makes the adjustment torque effective on this chuck body, that is an adjustment will tend to work in or against the rotation of the chuck body.
The rotation-canceling transmission is constituted as a two-stage codirectional transmission like a back-gearing transmission having central gears coupled together by two codirectional gears, the shaft rotatable about the central gear being supported dependent on the load on the output member of a torque coupling connected to the output of the adjustment drive motor. This electrical adjustment motor normally is driven in one direction at the same speed so as automatically to rotate the shaft about the main shaft of the back-gear transmission to compensate for the torque transmitted by the clutch and the clamping force.
In German patent document 3,218,083 and U.S. Pat. No. 4,573,379 of Hubert Bald a screw-type transmission is used to convert the input rotary movement into axial movement of the element that actuates the jaws or equivalent structure of the rotating machine tool being adjusted. The motor, once again, rotates continuously so that the tool is adjusted by varying the motor current. Once again the movement conversion involves forces that are applied between the working spindle carrying the machine tool and the part of it being moved so that any adjustment will probably entail some slight increase or decrease in rotational torque of the machine tool. Furthermore to achieve a particular adjustment torque it is necessary to adjust the electric feed to the motor in accordance with what speed the motor is running at and what rate the machine tool is rotating at. Thus it is necessary to use a controller taking into account the motor's operating characteristics and the chuck rotation speed as well as other factors. The result is therefore that this system is quite complex.